<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      /* focus 伪类选择器只在表单标签内生效 */
      input:focus {
        background: skyblue;
        color: white;
      }
    </style>
  </head>
  <body>
    <input type="text" name="" id="" />
    <br />
    <input type="text" name="" id="" />
    <br />
    <input type="text" name="" id="" />
  </body>
</html>
